1. The virus of yellow fever may be preserved for at least 154 days in the blood or liver tissue of infected monkeys if the material is dried in a vacuum while in the frozen state and kept in the refrigator in sealed glass containers. A gradual diminution of virulence is noticeable in the older specimens.

2. If infectious blood is dried in a vacuum at room temperature, instead of in the frozen state, and is stored in sealed containers in the refrigerator, the virus may survive as long as 155 days.

3. The virus may be preserved for at least 30 days in liver kept continuously frozen.

4. Storage of blood or liver in 50 per cent glycerine in the refrigerator will usually keep the virus alive for 60 days and may do so for 100 days, but with the injection of the older material there is a marked tendency toward lengthening of the incubation period and increase in the number of recoveries.

5. Yellow fever virus in citrated or clotted blood, when kept in the refrigerator, dies out rapidly.

6. In our experience the most satisfactory method of preserving strains of yellow fever virus in the laboratory consists of freezing and drying blood taken from a monkey on the first day of an attack of experimental yellow fever and storing the dry material in sealed glass tubes in a cold place.

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